This invention relates to a degree-of-stain-on-printed-matter examining apparatus for examining the degree of stain on the surface of printed matter, such as securities.
A conventional degree-of-stain-on-printed-matter examining apparatus examines the degree of stain on printed matter as follows. The apparatus causes image input means, such as a television camera or a line sensor, to pick up the surface image or transmitted image on one side or both sides of printed matter and input the image data, senses the leading edge of the printed matter from the inputted image data, takes in the image data from the whole surface of the printed matter, starting from the sensed leading edge, and compares the taken-in image data with the preset reference data, thereby determining the degree of stain on the printed matter.
One known method of calculating the degree of stain in such a degree-of-stain-on-printed-matter examining apparatus is to examine the degree of stain only in a specific area, such as an unprintable area, on the whole surface of the printed matter.
There has been no degree-of-stain-on-printed-matter examining apparatus for examining the degree of stain on the areas other than the unprintable area, that is, the degree of stain on the printed area. Accordingly, the conventional degree-of-stain-on-printed-matter examining apparatus has the problem of failing to examine the degree of stain which persons feel from the whole surface of printed matter.
The object of the present invention is to provide a degree-of-stain-on-printed-matter examining apparatus capable of examining the degree of stain on printed matter with as high accuracy as that of human senses.
In order to achieve the above object, according to one aspect of the present invention, there is provided an apparatus for examining the degree of stain on printed matter, comprising: image input means for inputting images including the image of printed matter to be examined and supplying image data on the printed matter; area information storage means for storing positional information on at least two target areas on a standard image corresponding to the image of the printed matter, the area of each of the target areas, their standard average densities, and the degree of dispersion in their density distribution; average density computing means for calculating the average density for each target area in the image data supplied from the image input means by using the positional information on each target area and the area of each target area supplied from the area information storage means; density difference measuring means for measuring the density difference between the average density for each target area calculated by the average density computing means and the standard average density for each target area supplied from the area information storage means; density difference normalizing means for normalizing the density difference for each target area by using the density difference for each target area measured at the density difference measuring means and the degree of dispersion in the density distribution for each target area supplied from the area information storage means; and summing means for summing the normalized density difference for each of the target areas supplied from the density difference normalizing means and thereby judging the degree of stain on the printed matter to be examined.
The apparatus of the invention further comprises: visual characteristic coefficient computing means for calculating a coefficient agreeing with human visual characteristics for the standard average density for each target area supplied from the area information storage means; and weighting means for calculating a degree-of-stain decision value for each target area by multiplying the normalized density difference for each target area supplied from the density difference normalizing means by the area of each target area supplied from the area information storage means, and further by the visual characteristic normalized coefficient supplied from the visual characteristic coefficient computing means, wherein the summing means includes addition means for adding the degree-of-stain decision value for each of the target areas supplied from the weighting means and judging means for judging the degree of stain on the printed matter by comparing the degree-of-stain decision value added by the addition means with a specific threshold value for the degree of stain.
The visual characteristic coefficient computing means determines the reflectivity corresponding to the standard average density for each target area supplied from the area information storage means and calculates the visual characteristic normalized coefficient on the basis of the ratio of the individual reflectivities.
The apparatus of the invention further comprises learning means which includes: storage means for receiving images of the printed matter as an object of learning from the image input means and storing the images of the printed matter; average image creating means for creating an average density value image on the basis of the images stored in the storage means; labeling means for putting the same label on the pixels included in the same density range on the average density value image supplied from the average image creating means; area extracting means for combining areas in the same density range where more than a specific number of pixels are consecutive on the images subjected to the labeling process by the labeling means, thereby extracting a target area on the printed matter, and supplying the number of the target areas and their positional information; area computing means for computing the area of each target area calculated by the area extracting means; and statistical value computing means for creating a density histogram for the average value image supplied from the average image creating means and calculating the average density and standard deviation for each target area, wherein the area information storage section stores the number of target areas and positional information supplied from the area extracting means, the area of each target area supplied from the area-by-area area computing means, and the average density and average standard deviation for each target area supplied from the statistical value computing means.
With the present invention, the degree of stain on the whole surface of printed matter (the degree of dirtiness persons feel from the whole surface of the printed matter) is judged by using the degree of stain on at least two target areas on the printed matter, the area of each target area, and a coefficient expressing how conspicuous stains are to human senses at the average density of each target area on the printed matter. At a result, the degree of stain on printed matter can be examined with as high accuracy as human senses.
Furthermore, pieces of printed matter can be arranged in the order of human senses, for example, in the order in which the cleanest one comes first and the dirtiest one comes last. Moreover, the degree of stain on one side and that on the other side can be evaluated and, on the basis of the evaluation, stains clustered only on one side can be examined.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.